How Did Mammals Develop Hearing? Study Examines Findings

A team of international researchers are shedding light on the evolution of hearing among mammals. In this latest study, led by the University of Queensland, the researchers focused on how mammals developed more sensitive hearing than reptiles. The development of the mammalian middle ear is a key element of the "extreme transformation" in the evolution of mammals from reptile-like ancestors.

However, previous theories regarding how and why have been based on insufficient data, according to the researchers.

"One of the problems with earlier studies on mammalian development is that scientists saw a relative shrinking in size of middle ear bones, as well as a movement away from the jaw joint, possibly under the influence of a rapidly expanding brain," Dr. Vera Weisbecker, coauthor of the study from UQ, said in a news release. "Because scientists look to such development processes to find out about evolution, these processes were interpreted to reflect the evolution over time of the mammalian middle ear."

Weisbecker claimed that patchy fossil records have not provided sufficient data to make such conclusions. Small numbers of fossil evidence would not allow scientists to find the details of how the mammalian middle ear actually developed. Mammalian evolution began 320 million years ago, three ancestral reptile-like jaw bones, which were designed for feeding were "retooled" for a new purpose of conducting sound more sensitively in the inner ear.

"It's not known why this change occurred, but it is thought that by extending their range of hearing to include high-pitched sounds, mammals could improve their detection of prey, such as small insects in the dark," Weisbecker said.

The researchers carried out their research by using data from marsupials and monotremes. They found that many previous theories about the mammalian middle ear development lack sufficient evidence to confirm on their claims. The researchers study revealed that there is a need for additional fossil evidence to confirm many of these evolutionary theories.